This application claims the priority of 196 47 127.3, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for automatically monitoring traffic, including analysis of back-up dynamics, in which traffic measuring data are recorded at several measuring points of the traffic network.
Methods of this type are customary in the field of traffic routing engineering for recognizing disturbances or back-ups. In such methods, data concerning the traffic situation (such as the traffic flow and the average vehicle speed) are recorded at measuring points, for example by means of induction loop systems and/or beacon systems, and the measured data are appropriately analyzed. In order to forecast back-up dynamics between adjacent measuring points, different traffic models were developed. Two serious difficulties occur, however, in the development and use of such traffic models. On the one hand, the determination of the model parameters frequently depends on outside influences, such as the momentary environmental and weather conditions. Thus, a parametric pattern of one model which was validated once may suddenly change profoundly for the same road section of the traffic network; for example, because the road is becoming increasingly wet. On the other hand, it is difficult to develop a model which is valid for the whole possible vehicle density range and for different traffic situations.
Conventional methods of this type are disclosed in the following publications: F. Busch, "Automatic Recognition of Disturbances on Expressways--A Comparison of Methods", Dissertation, Karlsruhe, 1986; K. Everts, et al., "Comments Concerning the Traffic Flow Analysis, the Detection of Disturbances and the Traffic Flow Prediction for Influencing Traffic in Outlying Areas", Forschungsgesellschaft fur Stra.beta.enund Verkehrswesen, FGSV-Bericht 358, 1992; J. Acha-Datsa and F. L. Hall, "Implementation of a Catastrophe Theory Model for the Incident Detection Component of an Intelligent Highway System", 12th Congreso Mundial IRF, Madrid, 1993, Page 579; G. J. Forbes, "Identifying Incident Congestion", ITE Journal, June 1992, Page 17; H. Zackor, et al., "Investigations Concerning the Traffic Flow with Respect to Capacity and in the Case of an Instable Flow," Forschung Stra.beta.enbau und Stra.beta.enverkehrstechnik, Volume 524, 1988; and L. Kuhne, "Traffic Flow on Highways", Phys. B1., 47 (1991), Page 201.
German patent document DE-0S 44 08 547 A1 discloses a method for detecting traffic and recognizing traffic situations in which traffic data, such as vehicle speeds, traffic volume and traffic density, are determined at several measuring points. From the traffic data of two neighboring measuring points which form a measuring section of a certain route length, traffic parameters are formed. Specifically a speed density difference is determined according to a predetermined relationship, a trend factor is formed from the relationship of the traffic volumes at the two measuring points, and a traffic volume trend of each measuring point is derived from the rise of the tangent of the time-dependent traffic volume course. These three traffic parameters are processed using fuzzy logic to recognize critical traffic situations in the measuring section in question. The result is utilized to generate corresponding control signals for alternating traffic lights.
German patent document DE-OS 43 00 650 A1 discloses a method for determining vehicle-type-related traffic flow data on roads. The number of passing vehicles and their lengths are detected in successive measuring intervals at different observation points, taking into account the driving direction, and the data thus obtained are analyzed to determine a density condition variable. The value of the density condition variable is compared with a limit value and the amount and the direction of the deviation from the limit value are used to draw conclusions regarding the start of a back-up, the existence of a back-up, or a clearing-out of the back-up.
An object of the present invention is to provide a method of the type mentioned above which, with a given measuring point distribution over the traffic network, can determine reliably the time-related and space-related change of traffic congestion, at relatively low expenditures.
Another object of the invention is to provide such a method which is suitable for predicting travel time and for automatically controlling traffic influencing systems.
These and other objects and advantages are achieved by the present invention, which uses plausible assumptions to continuously estimate the time-dependent positions of the upstream and downstream flanks of a traffic back-up, based on characteristic relationships which utilize the recorded traffic measuring data in a manner which is easy to analyze. In this case, the word "downstream" applies to the driving direction in a particular considered lane; that is, in the case of a back-up, the back-up direction pointing to the start of the back-up. The word "upstream" on the other hand, applies to the opposite direction; that is, in the case of a back-up in the considered lane, the back-up direction pointing to the end of the back-up.
An important advantage of this method is the fact that it operates reliably without any additional validation of the parameters, theoretically for unlimited distances between measuring points, in different traffic situation scenarios, such as different road conditions, in the form of wetness, snow, etc. In contrast, models which try to reconstruct the traffic flow by solving differential equation systems require a large number of validating parameters.
In one embodiment of the invention the selection of the two measuring points whose measured traffic data are entered into the analysis of the back-up dynamics appropriately follows the location change of a back-up. Thus, the traffic measuring data which are situated as close as possible to the back-up flanks are always used. This has an advantageous effect on the precision of the analysis of the back-up dynamics.
In another embodiment of the invention, the process is used for predicting the travel time for drives on back-up stressed traffic network sections.
Still another embodiment of the invention permits an adequate consideration of entry roads and exit roads which are situated between two measuring points of a road section and which, in turn, are provided with corresponding measuring points for traffic entering and exiting there.
Yet another embodiment takes into account a change in the number of lanes of a back-up stressed road section between the corresponding measuring points.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.